The statements in this section merely provide background information related to the present invention and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine or electric motor of the motor vehicle. An auxiliary pump may also be provided powered by a secondary prime mover, such as an electric engine, to provide fluid flow when the prime mover, and therefore the main pump, is turned off such as during stop-start engine control strategies. The valves and solenoids supplied with the hydraulic fluid are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
Some transmissions, such as hybrid electrical transmissions, require a high level of torque during launch. However, since the prime mover is off, the main pump is unable to provide the needed hydraulic fluid pressure levels. Accordingly, the auxiliary pump is used to fill the hydraulic circuits during launch. However, there is a constant need to reduce pump sizes in order to reduce cost, packaging size, and efficiency. Therefore, there is a need in the art for a hydraulic control system that augments hydraulic fluid flow while maximizing cost savings, reducing packaging size, and increasing efficiency of the main and auxiliary pumps.